The viability and severity of the childhood diagnostic category of attention-deficit hyperactivity disorder (ADHD) mandate research that can elucidate the nature of the psychopathology of this disorder. Indeed, its association with underachievement, peer rejection, and risk for delinquency render it a major public health concern. Comorbid aggression and antisocial behavior frequently accompany ADHD; understanding the development of both overt (fighting, defiance) and covert (stealing, property destruction) manifestations of such behavior is a crucial goal for the field. Although family interactional variables are not likely to be causal of ADHD symptomatology, they may relate to the development and intensification of comorbid overt and covert antisocial behavior. in addition, preliminary research of the PI reveals that the psychological variables of social cognitions and moral reasoning are linked to contemporaneous aggression, antisocial behavior, and peer rejection in this population. Through intensive family assessments, naturalistic summer research programs, and rigorous follow-up evaluations with ADHD and comparison boys aged 6-9 years, the PI will address the ability of such variables to predict the concurrent and subsequent display of overt and covert antisocial behavior and of peer status. Key predictors at the family level are maternal negativity with the child and indifference in attitudes towards child-rearing; at the child level, predictors include children's goals for social interaction and level of reasoning about moral dilemmas. Outcome measures feature validated naturalistic and laboratory observations of both overt aggression and covert antisocial behaviors, along with teacher ratings and self-reports of the same constructs. Another major aim is to detect the differential ability of two psychostimulants, methylphenidate (MPH) and dextroamphetamine (DEX), to effect change in ADHD children's aggressive behavior and in the responses of peers. The overall goals are to understand the familial and psychological factors that contribute to the considerable risk for poor long-term outcome in ADHD children and to appraise the amenability of comorbid aggression to pharmacologic intervention with two different stimulant agents.